Where are all the electrical experts?

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bigwow

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Posted this yesterday and not had one suggestion as to what the problem is and I've no idea where to start looking.

the anode on the starboard prop was completely gone; the one on the leg was almost untouched. On taking off the prop there was also a lot of play in the hub to spline joint, new prop last year.
On putting the screwdriver to the anode securing screw I got a slight shock, I hadn’t switched the engine switches off at this point.
Where do I start looking? The engines 12 yrs ago, came all wired up all I did was connect the live and earth.

John /forums/images/graemlins/shocked.gif
 
Not an expert, but logic says you have something connected to the earth strapping to that exhausted anode, which is using power.

Have you identified which battery bank is "working" when everything is formally switched off ?

Have you found any voltage indication at the point where you got the shock ? Is it AC (are you hooked up to shore power ?) or DC ?

Is this a new problem ? Have you connected any new devices recently ?

Trying to work through to find what is leaking power.
 
A shock! Over 50volts then.

The boat must have been connected to the mains, or had an inverter running. The anode was live relative to whatever else you were touching - another part of the boat, or standing on the ground. That suggests a reverse polarity connection somewhere, or a short or current leakage and no protection device.

Step 1 - disconnect mains, switch off inverters.

Step 2 - on boat, check the resistance between neutral and earth (should be zero or very low), and between live and earth (should be infinite). If neutral is not connected to earth on board, you're relying on the supply's earth.

Step 3. Unless you're very confident working with 230v, measuring voltages etc while one line is live, and you know enough about earthing and isolation to sort out what's live relative to what, on and off the boat, call an expert to look further and don't connect to the mains.

If your boat earth is internally connected to neutral, a strong possibility is that you're connected up to the mains with reverse polarity - ie, the neutral is live . . . and so's the boat. A very dangerous situation, especially in the wet. A mains tester plug will tell you if this is the case - a gizmo with three little neon lights . . .
 
On my Volvo saildrive, the leg had to be completely insulated fron the engine. No bonding (earthing wire) whatsoever allowed.
Could be yours has been somehow bonded. This would cause extreme deterioration of anodes and more worryingly, possibly erode the walls of the leg.
Hope this is of help and also that I am wrong.
 
Not a shock as such, more of a tingle. 240 supply was not connected at this time but the battery supply to the engine was. Nothing new electrically has been fitted as for how long it’s been like this I don’t know but I didn’t come across it when I changed the anodes last year but the 12V to the engine was more than likely switched off.
I only came upon it this year because I took the props off before going aboard to switch off.
 
On my boat the battery negative (which I'm guessing is the earth you refer to) is connected to the engine block, and therefore there is an electrical circuit through to the anode via the propshaft. Though a previous post mentioned that on their boat it is necessary to isolate them, so the arrangement on mine is not always the case. If your boat has an electrical connection through to the shaft, then the shock may have been caused by the potenial difference (voltage) between the battery negative and you (or the ground you were standing on).

Do you have a multimeter to check continuity and voltages? It may be worth spending an afternoon tracing all the wiring and draw a diagram.
 
Unlikely to be anything to do with the engine as Volvo inserted an insulating gasket between the engine and gearbox.

Is the play between the shaft and the splines in the hub of the prop. If so you need to check which is worn. If it is the prop rather than the shaft then it seems like a prop problem (as does the fast eroding anode). As only one year old go back to Volvo. They have plenty of experience on prop problems on Saildrives.
 
I was told that the Yanmar saildrive splines are not machined to standard and for instance Gori prop hubs do have play on them.
 
I’ve just remembered in late summer this engine would not start, the auto electrician traced the fault to the relay, on the negative side, located under the fuse box, Volvo 2002, and replaced it with a Lucas one from his van. I asked at the time was there anything different apart from the green paint, he said no. Could this be the problem?
 
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I doubt it.

Still puzzled by your claim to have connected "live and earth". I think a little more detail here would help?

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The engine comes pre wired with little tags on saying where to connect the live battery lead and where to connect the negative battery lead, these leads haven’t changed since the engines were fitted 12 yrs ago.
 
I was only questioning something you said in your first post.

Ah - I see - you don't mean you connected live and earth together! (Sorry, I was being a bit thick there! /forums/images/graemlins/blush.gif)
 
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Unlikely to be anything to do with the engine as Volvo inserted an insulating gasket between the engine and gearbox.

.

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Do you know why they do this? Seems a bit odd since we do exactly the opposite with a shaft drive.
 
You didn't state if the boat was out of the water at the time

If I got a tingle from touching any bare metal object, the first thing I would do is to measure the voltage of the bare metal object. Connect the voltmeter between the bare metal object and earth. Start by setting the voltmeter for measuring AC and note any reading. Then switch to the DC scale and read again. If you read a voltage on the AC scale, but not on the DC scale then the voltage is AC. If it is high (like 230V) you have a serious wiring problem or electrical fault somewhere. If the voltmeter reads on the DC scale, then it is probably a DC voltage leak somewhere. But to have felt an electric shock would definately require more than 12 volts DC. Hard to figure. Were you standing on the ground at the time?
 
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Rare for 12v to give a detectable tingle. You must have had a couple of wet hands,

[/ QUOTE ]Yes, wet hands and sensitive from the cold could well result in a tingle. I remember my father lying over his huge Exide batteries getting a very disconcerting shock - he had no shirt on, and it was very hot and sweaty, in the Med. But, as you say, 50V is normally regarded as the threshold.
 
We had just craned out so hull was wet; I was sitting on a plank. 240V was disconnected so has to be 12V my hands were wet and very cold.
 
Is there a capacitor somewhere in the system? That could give the effect you describe - sometimes fridges which are switched off will do it.
 
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